Abstract/Project Summary Youth sports participation has numerous positive mental and physical health benefits. During adolescence, an increased injury rate has been reported, potentially related to effects of rapid physical growth (growth spurts) on dynamic movement and a phenomenon called adolescent motor awkwardness. Injury to a young athlete results in millions of emergency room visits and millions of dollars spent every year and negates many of the positive benefits gained by participation in sports. There is a critical lack of evidence to support effective strategies for training and injury reduction in adolescence, as well as how to measure the degree and impact of adolescent motor awkwardness using quantitative measures of movement biomechanics. We propose to characterize adolescent motor awkwardness using a biomechanical model of gait of gait dynamic measures of smoothness and stability with perturbation during treadmill locomotion. Through this study we will: analyze gait smoothness and stability in adolescents in relation to three-month growth rate (Aim 1) during the ages when motor awkwardness is commonly reported; assess the relationship between muscle fatigue and gait smoothness and stability (Aim3); and analyze recovery patterns following perturbation of gait in adolescents (Aim 3).